This invention relates to a recording medium conveyance device for conveying a recording medium to have an image recorded thereon and an ink jet recording apparatus using this.
In a recording apparatus of an ink jet method in which image recording is carried out by jetting of ink drops to a recording medium, in order to record a high-quality image without generating a deviation of an image and a blur of the colors, it is important to maintain the accuracy of conveyance of a recording medium at a high level.
Up to this time, as regards such a technology for practicing the conveyance of a recording medium with a high accuracy, as described in the publication of the Japanese unexamined patent application H11-240654, it has been known, a conveyance device for conveying a recording medium by means of a conveyance roller (a capstan roller) and a pressing roller (a pinch roller) wherein, by protrusions having a convex shape of a height of 60 ± 40 μm and a diameter of 0.5±0.2 mm being arranged on the surface of the conveyance roller over a half or larger part of the surface area, the force to hold a recording medium by the conveyance roller and the pressing roller is strengthened, and the accuracy of conveyance is secured.
In a conventional recording medium conveyance device, there has been a problem that the quality of an image to be recorded is degraded if the conveyance length (that is, the length of one step of an intermittent feed) of a recording medium varies owing to a change of the thickness, the kind of the recording medium; therefore, it is necessary to adjust minutely the conveyance length by the conveyance roller. Usually, a stepping motor is used as a driving motor of the conveyance roller, and it is put into practice to adjust the conveyance length by changing the drive pulse. However, it is impossible to adjust the conveyance length by an amount smaller than the resolving power of the driving motor, and it has not been possible, by minutely varying the conveyance length of the recording medium, to practice an adjustment of the conveyance length to cope with the minute change of the thickness, the kind of a recording medium.
Further, in many cases, an image recording for a recording medium is carried out in the following way. That is, two sets of a conveyance roller and a pressing roller are provided with a recording means for recording an image put between the two sets, both the conveyance rollers are driven by one and the same driving motor, and a recording medium is stretched between the two sets of rollers. However, there is a problem that, even if both the conveyance rollers are driven by one and the same driving motor, owing to a variety of factors such as the deviation of the diameter of the conveyance rollers and the transmission loss of the driving force, a minute difference is produced in the conveyance length between the conveyance rollers, which produces a slack of the recording medium, or causes the recording medium to be pulled excessively by one of the conveyance rollers, and this influences the quality of an image to be recorded. Because it is impossible to adjust the conveyance length by an amount less than the resolving power of the driving motor, it has been impossible to adjust the conveyance length of a recording medium through minutely varying the conveyance length, to get rid of a slack or an excessive stretch of a recording medium.
Further, concerning the manufacturing of conveyance rollers, there has also been a problem that, in cases where a roller has a diameter variation in its axial direction, the conveyance length of a recording medium becomes different depending on the position in the axial direction, which causes a conveyance skew or a slack of a recording medium to be produced.